NADPH-DIAPHORASE ACTIVITY AND ITS COLOCALIZATION WITH TRANSMITTERS AND NEUROPEPTIDES IN THE POSTGANGLIONIC NEURONS THE RAT SUPERIOR CERVICAL-GANGLION

NADPH-diaphorase activity (NADPH-DA), a marker of neural nitric oxide synthase, was found in many postganglionic nerve cell bodies in the ad ult rat superior cervical ganglion (SCG) after colchicine treatment, p ostganglionic nerve trunk ligation or ganglion culture. NADPH-DA coloc alized with immunoreactivity to tyrosine hydroxylase (TH), serotonin, vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), methionine- enkephalin and somatostatin. Almost all cells showing NADPH-DA were TH -immunoreactive, although several TH-immunoreactive cells lacked NADPH -DA. While suggesting that nitric oxide has an important role in the n euronal modulation in the synaptic transmission in the rat SCG, our re sults point out that nitric oxide synthesis is confined to a subpopula tion of ganglion neurons. Our findings confirm the idea that the super ior cervical ganglion consists of several subpopulations in which nora drenaline is colocalized with other transmitter or neuropeptide. Only about one-fourth of serotonin-immunoreactive neurons contained NADPH-D A. Similarly, the neuropeptides studied showed only partial colocaliza tion with NADPH-DA. Our results thus suggest that nitric oxide is not associated with any particular transmitter or peptide.